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Fri, 23 May 2025 09:18:45 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id TdfLLHU9MGhcPQAAD6G6ig (envelope-from ); Fri, 23 May 2025 09:18:45 +0000 Date: Fri, 23 May 2025 11:18:36 +0200 From: Oscar Salvador To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux.dev, "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , "Matthew Wilcox (Oracle)" Subject: Re: [PATCH v2 1/1] mm/memory_hotplug: PG_offline_skippable for offlining memory blocks with PageOffline pages Message-ID: References: <20250520164216.866543-1-david@redhat.com> <20250520164216.866543-2-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 63AC6140008 X-Stat-Signature: crfaimb6mmbqge677r4tiz4fe66q1obf X-Rspam-User: X-HE-Tag: 1747991928-27791 X-HE-Meta: U2FsdGVkX1+SB6go7VEYv6vIbJVxA8N441x3OQ9Zm6iJQYam0AkkSXtc7LyVjnHPjr6tYfM1DMyvLUuVI9mEa6tQxBxjqhit4QznN9HVIwFIm2Ajk9U0/rQ/hsXQnLIJ2qevAqKZVGR744OrWycnCtTUsmSfqcmZWEL+2B4n7jtaOqwq8zeS1KFhiz/QvMchld+Q7nUs82niCWCiaZ5YNeeQbThSqvYmaQ22ojW9Z30TWRF70s+1wA1vwqPgVNyW+hmQg1iPZV6AFt2occGrAd92KScRYmpbJreP+utFGhXpE56S4skS9raMS9I0vD78NsnvO4edG2on9gInl6KChMkhLCwulci9h+Y3Aa2DtdFU5YQkMYh02MBSiXLX9THEQic9qCrYn5Vj/GgrAIhsO+MJxwfzm5KLYHK7gCyS0J8EMT45qZ2WeiM/WYRgex0OjvumJkqOzTiYIT75rgziGPIzFHzlhG26Yg91sluirLOUMyr7St39sUQhJvhQhgJroOGGQ7q8U0BCWHUkQVdbvbK7Ejx2izkl9K30Qm7Nuk1P3F4GoxEGTeVPjKZbhc6pzHQC0hU8qxZZeatA6+D8SzCIoB/xlmKQq/hkAqJ0qy62BX2ZRChEFSfEokT+8BeKPRARNJWtfaePAKVjH0OuH4ekI2LNkWNVvHJyAt/yK3TIJITm+d3Md2+js56iT2TodDDrwX2GPeIyJJXU/4s6tw2fdPHhaBr0a4CJ9JVaX1zHUK/1tbtZK3za3qD5t3XhjPQXYLZhfM6hjBThgFMEOmSncK9odCrh8K4yYXLl6nDEqAwM/n73Tw8I7B5oAY1H7uMfqa+Y4vxmF4ScJgiuzOxggJfmaPGW7rEcF4ex1ONM4QFjFHoWyvzMqSfviSnwWGHXuoRHQ6HPfB+fMV3AYSUAJmeoMhUzB5YJ4fD4jx2zUNl4ZPfDgW+KxISXAM0HmRaKN3by0GCO1Nj8wxI UvOGYEJy 1wBtZ0YIJYTpLv9+ChtkhhKyxdB02ZD2Sjl5hKHICqCJGLlkMKZoCQjYEc1RHi2syHB2rSkYQmyx3NTKL4KirYM1Wyhjatvun+D0W7usjW/JRk4n8Bx16xKxiFGeIYMU/+LPg3vT2pAlvcZmKMMn1BNnL24RbvD+PlVRFoCsmZlDYcpa7XauwKjhZmkcrIsg6Jr6uESMG1guhiqhanzKnbl5B5bVCdW/zdp/LC+ZgQwdSMwYAtXfLm7V4fG+PE/8N35QD4bRVR9Gw7vUsoFBc6LutqktPAIudo7i4oH1u8iHy/oSBRbCOKnQuKw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 21, 2025 at 03:44:32PM +0200, David Hildenbrand wrote: > No, the code is confusing. > > All pages are PageOffline. Only the ones that have not been onlined are *in > addition* PageDirty. > > The relevant bit is documented in page-flags.h: > > "When a memory block gets onlined, all pages are initialized with a refcount > of 1 and PageOffline(). generic_online_page() will take care of clearing > PageOffline()." Ah ok, I see it in __free_pages_core(). > > - If we want to release logically-offline pages belonging to an onlined memory-block, > > we ClearDirty them and be done > > PageOffline gets cleared in both cases: See the comment in > virtio_mem_clear_fake_offline() > > "/* generic_online_page() will clear PageOffline(). */" > > I'll note that I am planning on removing that PageDirty() handling > completely, and also letting handling PageOffline() clearing be always > performed by memory freeing core (the latter is easier to achieve). Cool, I think that would be much clearer. > When re-onlining, the core will set them all PageOffline, and virtio-mem > will intercept page onlining using the page_online_cb. > > virtio-mem will then online the actually plugged parts (-> > generic_online_page(), which clears PageOffline and exposes them to the > buddy) and set the unplugged/hole parts as PageOfflineSkipabble again. > > That logic resides in virtio_mem_online_page_cb(). Sorry, I had to re-cache this. Ok, I think that now I caught up with the code. I see that we mark it Offline in memmap_init_range(), and then __free_pages_core() will clear the flag before releasing them to the buddy. Ok, I think it is much clear now, thanks for helping me out with the details! -- Oscar Salvador SUSE Labs